1. Field of the Invention
The present invention relates generally to semiconductor component fabrication. More particularly, the present invention relates to methods of forming vias of varying lateral dimensions for use in semiconductor components and assemblies.
2. State of the Art
Conventional semiconductor components, such as semiconductor dice, have external contacts that enable electrical connections to be made from an active surface of the semiconductor die to the integrated circuits formed on or within the active surface. For instance, semiconductor components may include external contacts in the form of discrete conductive elements, such as conductive balls or bumps, formed in an array on the die itself, or discrete conductive elements, such as wire bonds, extending from the active surface to terminals of an interposer substrate of the component or directly to a carrier substrate, such as a printed circuit board.
In other packaging configurations, test carriers for testing a semiconductor component, such as a bare semiconductor die or a chip scale package (generically termed “device under test,” or “DUT”), often include contacts for making temporary electrical connections to external contacts, such as bond pads or conductive bumps, on the semiconductor component being tested. The test carriers also include contacts such as pins or pads for routing electrical connections from the DUT to a test board and associated test circuitry.
However, an inner lead bond (ILB) pattern on the active surface of a semiconductor die may include contacts in the form of bond pads, which are very small, i.e., 100 microns square, very closely spaced or pitched (typically along or adjacent a center line of the die or along a periphery of the die) and, as a result, are difficult to align with and electrically contact because of their relatively small size. Thus, wire bonding may be difficult, as may probe testing or burn-in of the semiconductor die.
To electrically connect to the small contacts in the ILB pattern, the contacts in the form of bond pads of the ILB pattern may be redistributed to other locations on the active surface using a redistribution layer (RDL). The RDL comprises a plurality of conductive traces extending from the bond pads of the ILB pattern to redistribute the contact locations of the ILB pattern to an outer lead bond (OLB) pattern that includes terminal pads that are about 240 microns square, more widely pitched and, thus, easier to electrically contact. However, the formation of the RDL traces and redistributed contact pads requires at least one extra step in the fabrication process of a semiconductor die and adds time and expense to the fabrication process.
Another method of providing external electrical contacts to integrated circuitry of a semiconductor die is to form vias extending between the active surface and the back side of the semiconductor die (typically while the die is at the wafer level and in conjunction with the formation of vias in all of the semiconductor dice of the wafer or other bulk substrate) and to fill the vias with a conductive material. However, one problem of conventionally providing vias through semiconductor dice from an ILB pattern is that the size and pitch of the bond pads have been continually decreasing while the total number of bond pads on a single semiconductor die has been continually increasing due to ongoing advances in semiconductor fabrication and increased circuit complexity. For example, a chip scale package can include a hundred or more external contacts, each having a lateral extent of about 10 mils and a pitch of about 30 mils. While it is possible to reroute the ILB pattern on the active surface of a semiconductor die and then form vias through the semiconductor die substrate from redistributed contact locations to the back side thereof, such an approach is self-defeating as still requiring an RDL extending to the via locations. Further, there may not be sufficient space, or “real estate,” on the active surface to provide sufficient redistributed locations for vias.
Accordingly, efficient back side connection of small, densely pitched bond pads on semiconductor dice using conventional techniques requires correspondingly small and densely pitched conductive vias. However, such conductive vias can be difficult to form, to align with the pads of the ILB bond pattern and to fill with a conductive material. Moreover, processes useful for filling small vias, such as chemical vapor deposition (CVD), sputtering, electroplating, and electroless plating, are relatively slow and may result in voids, or “keyholing,” within a via, resulting in a poor or defective electrical path.
Accordingly, a need exists for a method of fabricating through-hole vias that are easy to connect to bond pads of an ILB pattern while still efficient to form and conductively fill. Further, it would be desirable to have the ability to form a through-hole via that exhibits a larger cross-sectional area or dimension on one side (for example, a back side) of a semiconductor component, such as a semiconductor die, and is effectively more widely pitched from any adjacent via to facilitate connection to another semiconductor component while exhibiting a smaller cross-sectional area or dimension on the opposing side (for example, an active surface) of the semiconductor component directly connected to a bond pad of an ILB pattern.